Enzymes, which are produced by, and are obtained from, living cells (e.g., bacteria), have become a common component in various compositions, including industrial and consumer applications and cleaning compositions, such as laundry detergents, laundry presoak and pretreatment products. Enzyme compositions are used to break down organic materials such as proteins, starches and fats into smaller molecules that can be more easily solubilized or dispersed in an aqueous liquid. Some uses for enzyme compositions for cleaning include laundry detergents, fabric softeners, all types of wipes, liquid dishwashing products (manual or automatic), and hard surface cleaners. Enzymes for use in personal care formulations include facial, skin and body care products, where proteases enhance various macromolecular maturation or hydrolytic functions. Enzymes are used for a variety of bio-processing uses such as converting grains into sweeteners, fermentation, converting biomass into ethanol for fuel, and enhancing animal feed for livestock and pets. In the pulp and paper industries, xylanases are used for bleach boosting, cellulases for refining pulp and paper recycling, and amylases for starch removal and modification. Other industrial uses of enzymes include the industrial biotech production of chemical products, plastics and fibers. Enzymes have also been developed for the bioremediation of industrial and agricultural wastes, decontamination of chemical toxins, and maintenance of processes by biofilm removal.
The largest volume of enzymes is currently for use in detergents and cleaners, where detergent enzymes generally exhibit hydrolytic activity under alkaline conditions. Detersive compositions frequently contain active proteases (i.e., proteolytic enzymes); they also may contain amylolytic enzymes that break down starch-containing soils. Other enzymes compositions use lipase enzymes or cellulolytic enzymes, typically in combination with a protease or amylase. Although detergent formulators select these enzymes for their ability to remain active in aqueous detersive systems, the proteolytic, amylolytic and other enzymes commonly employed in detersive compositions may exhibit loss of activity (i.e., instability) during storage.
The loss of enzyme activity is more pronounced in liquid or gel compositions. Enzymes may be destabilized by unfolding of the three-dimensional structure of the enzyme or by enzyme breaking down. Common destabilizers include polar solvents like of water or other solvents, microbial attack, electrolytes, charged surfactant, temperature and extreme pH. Stabilizers are added to rigidify the structure of the enzymes include boric acid, glycols, small organic acids, and calcium chloride. In addition, proteases have a tendency to attack themselves and other enzymes, causing autolysis and proteolysis in the formulation. Formulators inhibit protease with protease inhibiting materials such as boric acid, boronic acids, proteinaceous materials, borate esters of vicinal polyols, for example monopropylene glycol with sodium borate
In order to compensate loss of enzyme activity during periods of storage, formulators may use excess enzymes in liquid enzymatic compositions such as detergents. However, enzymes are relatively expensive formulation ingredients; accordingly, formulators may employ enzyme stabilizers in liquid compositions to inhibit autolysis of the protease and other enzyme destabilization reactions.
Materials that have been used for stabilizing enzymes include various organic and inorganic compounds such as polyols, carboxylic acids, carboxylic acid salts, carboxylic acid esters, and sugars; calcium salts; boron compounds, and various combinations thereof. Protein extracts can also be used to stabilize enzymes through inhibition of the enzyme.
U.S. Pat. No. 5,221,495 discloses a three-component enzyme stabilization system for liquid detergent compositions including a boron compound, a hydroxypolycarboxylic acid having two or three carboxylic acid groups and from 1 to 4 hydroxyl groups, and a calcium salt. The hydroxypolycarboxylic acid is preferably citric acid.
U.S. Pat. No. 4,842,758 discloses detergent compositions containing an enzyme that is stabilized by a combination of ingredients, including an alpha-hydroxy-carboxylic acid or an alpha-hydroxy-poly-carboxylic acid, a boron compound, and a proteinaceous material, e.g., casein. The patent discloses as examples maleic acid, tartaric acid, lactic acid, and citric acid, with citric acid being most preferred. This patent teaches that the proteinaceous material is essential to inhibit the protease and thus stabilizes both the protease and amylase enzymes. This patent teaches that, without the proteinaceous material, it is impossible to stabilize the enzymes used in the system. The amount of proteinaceous material in the compositions is relatively high, at 1 to 6 wt. %, compared to 1 to 5 wt. % of alpha-hydroxy carboxylic acid, and 0.5 to 2.5 wt. % of boron and 0.5 to 3 parts by weight enzyme. This patent teaches mixing alpha-hydroxy-acid with Borax (Na2B4O7.10H2O), adding casein dissolved in NaOH solution, and then adding this mixture to the enzyme. Furthermore, this patent teaches the use of phosphate salt builders in levels in excess of 5%.
U.S. Pat. No. 5,691,292 describes a dishwashing detergent composition containing an active enzyme and an enzyme stabilization system comprising at least one stabilizing agent selected from the group consisting of calcium ion, boric acid, propylene glycol, short chain carboxylic acids, boronic acid, polyhydroxyl compounds and mixtures thereof. It is disclosed that suitable polyols contain from about 2 to about 6 carbon atoms and from about 2 to about 6 hydroxyl groups. The patent teaches specific examples such as propylene glycol, with 1,2-propane diol being preferred, 1,2-butane diol, ethylene glycol, glycerol, sorbitol, mannitol and glucose. The patent also teaches the option of adding carboxylates, including formates, to the compositions, and that sodium formate is preferred. The patent also teaches the option of adding detergency builders such as citric acid or an alkali metal citrate (e.g., sodium citrate) to the dishwashing detergent compositions. The patent includes sodium citrate (as a detergency builder), and an enzyme stabilization system consisting of one or more of the following ingredients: boric acid, 1,2-propane diol, calcium formate and sodium formate as an exemplary dishwashing detergent compositions.
U.S. Pat. No. 4,462,922 describes an aqueous enzymatic liquid detergent composition containing an enzyme stabilization system. The enzyme stabilization system comprises boric acid or an alkali-metal borate, a polyol, and an antioxidant that is a reducing alkali-metal salt. This patent teaches that the polyols that can be used contain from 2 to 6 hydroxyl groups. The listed polyols are ethylene glycol, propylene glycol, 1,2-propane diol, butylene glycol, hexylene glycol, glycerol, mannitol, sorbitol, erythritol, glucose, fructose, lactose and erythritan.
U.S. Pat. No. 5,468,414 discloses liquid detergent compositions containing an alpha-hydroxy acid builder, a surfactant, a proteolytic enzyme, a second enzyme, and an enzyme stabilization system comprising a mixture of certain vicinal polyols and boric acid or its derivatives. This patent teaches built liquid detergent compositions containing an alpha-hydroxy acid builder such as tartrate mono-succinic acid or citric acid. This patent teaches that alpha-hydroxy acid builders are detrimental to enzymes stability, consequently, they teach use of specially selected vicinal polyols in combination with boric acid or its derivatives as an enzyme stabilization system.
U.S. Pat. No. 5,976,556 describes skin conditioning compositions containing an acid protease which is enzymatically active below about pH 5.5 and which is significantly inactive at or above pH 5.5, and an acidic buffer comprising an inorganic acid. This patent teaches the uses of organic acids including alpha-hydroxycarboxylic acids such as lactic acid, citric acid, glycolic acid and malic acid to reduce skin pH, but does not teach an enzyme-stabilizing complex.